The invention refers to an apparatus for processing synthetic plastics material, in particular thermoplastic synthetic plastics material, comprising a receptacle, in the bottom region of which a comminuting and mixing tool is disposed rotatably around a substantially vertical rotation axis, and a screw-type extruder conveying the material out of the receptacle, the inlet opening for the material of this screw-type extruder being disposed at one front side of the screw and being formed by an opening in the side wall of the receptacle, which opening is disposed substantially at the level of the comminuting and mixing tool, no or no substantial parts of the screw-type extruder protruding from the inner wall of the receptacle.
Such apparatus are known (EP-A 123,771). The synthetic plastics material delivered to the receptacle is comminuted by the rotating comminuting and mixing tool and is brought into a vortex circulation, the synthetic plastics material being heated by the thereby exerted cutting and friction energy. Since big, not comminuted parts are heated more than already comminuted material, a mixture with sufficient good thermic homogenity results during the comminuting and mixing process. This mixture is conveyed out from the receptacle by the screw-type extruder and is plasticized thereby. Disposing the screw type extruder at the level of the comminuting and mixing tool is substantially more favourable than another known disposition in which the screw-type extruder is disposed spaced above this tool, a guide wall protruding inwardly from the inner wall of the receptacle guiding the circulating material into the inlet opening of the screw-type extruder, because the latter embodiment implies a multiple turning of the comminuted material before it can be catched by the screw. Further, the screw protruding into the interior of the receptacle as well as the guiding wall disturb the vortex circulation, which results in an inhomogeneous mixture and causes the danger of blocking the rotating tool, particularly when treating big particles of the material.
Within another known apparatus (FR-A 2,418,707) the screw-type extruder is disposed tangentially with respect to the receptacle. The inlet opening for the material is disposed substantially in the center of the length of the housing of the screw, which results in the disadvantage that catching the material by the screw-type extruder is not assisted by the centrifugal forces acting on the particles of the material, because the particles of the material must change their moving direction nearly perpendicularly. Further, this embodiment shows substantial dead corners, in which the material can gather and may block the rotation of the tool.
The initially described known embodiment in which the axis of the screw is disposed radially with respect to the receptacle, shows a sufficient filling of the screw for material which can be charged well. In many cases, however, an increased filling of the screw is desired, particularly then, if stretched, very strong synthetic plastics materials shall be treated or such kinds of synthetic plastics material which must not be pre-densified by heat influence due to their heat sensitiveness in the presence of oxygen. It would be imaginable to get an increased screw filling by providing a large conus-like enlargement of the intake section of the screw, however this results in high costs for the screw provided with a large diameter and in an increased wear of it due to the increased circumference velocity.
Another possibility known from the initially described embodiment consists in assisting the supply of the material into the inlet opening of the screw-type extruder by providing the comminuting and mixing tools with a sickle-shaped, backwardly curved shape so that they act like a spatula, the material thereby being forced into the inlet opening of the screw housing to an increased extent. However, also this is not sufficient when treating certain kinds of materials.